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Thyroid

Reverse T3

Reverse T3 is an inactive thyroid hormone that may increase during overtraining, underfuelling, or physical stress. For active individuals, elevated levels might indicate the body is conserving energy by reducing active thyroid hormone availability.

Doctor's Assessment Included

Reference Ranges

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

Male Your group
pmol/l
Low 0.14 Normal 0.54 High
Female Your group
pmol/l
Low 0.14 Normal 0.54 High

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Check your own value

What It Measures

This test measures the level of reverse triiodothyronine (rT3) in your blood. Reverse T3 is produced when the body converts T4 into an inactive form instead of active T3. It may serve as an indicator of how your body is prioritising thyroid hormone utilisation.

Why It Matters

For active individuals, elevated Reverse T3 may signal that the body is under excessive training stress or caloric deficit. Some sports medicine providers use it to detect early signs of overtraining syndrome. Addressing elevated levels might help restore performance and recovery capacity.

When to Test

Some people may consider testing Reverse T3 when experiencing persistent fatigue or symptoms of low thyroid function despite normal TSH and T4 levels. It might be useful during periods of chronic stress or illness. Your healthcare provider can advise on whether this test is appropriate.

Symptoms

Low Levels

Low Reverse T3 levels are less commonly discussed, but some healthcare providers note that very low levels may occasionally be seen alongside hyperthyroid states. Symptoms might overlap with those of an overactive thyroid. Discuss any concerns with your healthcare provider.

High Levels

Some people with elevated Reverse T3 levels may experience fatigue, brain fog, weight gain, or cold intolerance despite normal T4 and TSH readings. High levels might suggest the body is under significant physiological stress. Your healthcare provider can help interpret these results.

Recommendations

Male

If Low

Low reverse T3 is generally not concerning.

If High

Elevated reverse T3 may indicate stress, illness, or a conversion issue. Consider investigating underlying causes.

Female

If Low

Low reverse T3 is generally not concerning.

If High

Elevated reverse T3 may indicate stress, illness, or a conversion issue. Consider investigating underlying causes.

Lifestyle Tips

Some people may help support healthy Reverse T3 levels by managing chronic stress, avoiding extreme caloric restriction, and prioritising sleep. Adequate nutrition with sufficient iron and selenium might also play a role. Always consult your healthcare provider before making changes.

Frequently Asked Questions

What causes Reverse T3 to become elevated?
Elevated Reverse T3 may result from chronic stress, severe illness, caloric restriction, or inflammation. Some healthcare providers suggest the body produces more Reverse T3 as a protective mechanism to slow metabolism during challenging periods.
Is Reverse T3 testing routinely recommended?
Reverse T3 is not typically part of standard thyroid panels. It is sometimes ordered when a healthcare provider suspects a conversion issue or when symptoms persist despite normal TSH and Free T4 levels. Your provider can determine if it is appropriate for you.
Can dieting increase Reverse T3 levels?
Some research suggests that significant caloric restriction or prolonged dieting may increase Reverse T3 levels as the body attempts to conserve energy. This is sometimes referred to as adaptive thermogenesis. Discuss dietary concerns with your healthcare provider.

Tests with related values

These panels measure values from the same category as this marker.

Complete Health

360 Health

Broad health panel: hormones, thyroid, vitamins, lipids, liver, kidney, and blood count.

HbA1c (Glycated Hemoglobin) TSH (Thyroid Stimulating Hormone) Triglycerides Urea (BUN) Creatinine eGFR (Estimated Glomerular Filtration Rate) Free T4 (Thyroxine) LDL Cholesterol Liver Function Test (LFT) SHBG (Sex Hormone Binding Globulin) Vitamin B12 Vitamin D (25-OH) Total Testosterone Free T3 (Triiodothyronine) Ferritin HDL Cholesterol Albumin Total Cholesterol Basic Blood Count
€346,-
Health Checkups

InsideTracker

A 36-biomarker performance and longevity panel inspired by InsideTracker Ultimate — covering heart, hormones, metabolism, inflammation, recovery and iron status.

SHBG (Sex Hormone Binding Globulin) TSH (Thyroid Stimulating Hormone) ALT (Alanine Aminotransferase) LDL Cholesterol GGT (Gamma-Glutamyl Transferase) Cortisol DHEA-S Estradiol (E2) Free Testosterone Total Testosterone Folate (Folic Acid) Vitamin B12 Calcium Ferritin Iron (Serum) Magnesium Magnesium (Intracellular) Potassium Progesterone Sodium Transferrin CRP (C-Reactive Protein) Glucose (Fasting) HbA1c (Glycated Hemoglobin) ApoB (Apolipoprotein B) HDL Cholesterol Total Cholesterol Albumin AST (Aspartate Aminotransferase) Vitamin D (25-OH) Insulin (Fasting) Leukocyte Differential Creatine Kinase (CK) Transferrin Saturation Triglycerides Basic Blood Count
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Whoop

A 44-biomarker comprehensive health panel inspired by WHOOP Advanced Labs — a deep look at metabolism, cardiovascular risk, hormones, liver, kidney and inflammation.

SHBG (Sex Hormone Binding Globulin) TSH (Thyroid Stimulating Hormone) ALT (Alanine Aminotransferase) LDL Cholesterol Cortisol DHEA-S Estradiol (E2) Free Testosterone FSH (Follicle Stimulating Hormone) LH (Luteinizing Hormone) Total Testosterone Bicarbonate Calcium Chloride Ferritin Iron (Serum) Magnesium Potassium Sodium Transferrin CRP (C-Reactive Protein) Homocysteine Glucose (Fasting) HbA1c (Glycated Hemoglobin) ApoB (Apolipoprotein B) HDL Cholesterol Omega-3 Index Total Cholesterol Albumin HOMA-IR ALP (Alkaline Phosphatase) AST (Aspartate Aminotransferase) Bilirubin (Total) Total Protein Urea (BUN) Creatinine Vitamin D (25-OH) eGFR (Estimated Glomerular Filtration Rate) Insulin (Fasting) Leukocyte Differential Transferrin Saturation Lipoprotein(a) Triglycerides Basic Blood Count
€499,-

Reverse T3

€130,-